This invention relates to electrical mortar firing systems eminently suitable for use in heat-seeking missile-decoy systems.
Such missile decoy systems commonly comprise infra-red mortars which may be fired in succession from suitable launching means carried by the potential missile target and arranged to generate infra-red radiation at progressively increasing distances from the target.
The infra-red mortars may be stacked end-to-end in multiple mortar (e.g. seven) packs arranged to be electrically coupled within the barrel of mortar launching means to electrical mortar firing means.
The electrical mortar firing means may comprise an inductive coupling arrangement through which mortar firing pulses (i.e. bursts of a.c. of predetermined duration) are transmitted. The pulses are utilised, after rectification thereof by means of a full-wave rectifier, to step an electro-magnetic stepping switch which applies the pulses in turn to the igniters of the respective mortars of the pack as the switch is stepped from one position to the next. These pulses are applied to the igniters of the respective mortars over pairs of wires which extend from the firing means which is located at the base of the launcher barrel to the individual mortars of the multiple pack. On arrival of the first mortar firing pulse over the inductive coupling arrangement the stepping switch is operated to apply a proportion of the incoming pulse over an appropriate pair of wires to the igniter of the mortar located at the top end of the multiple pack. The top-most mortar is accordingly fired from the launching barrel and a pyrotechnic time fuse is simultaneously ignited which causes the mortar to generate infra-red radiation after a predetermined delay from launch.
The next mortar firing pulse to arrive will normally cause the stepping switch to step to its next outlet position at which it applies a proportion of the incoming pulse over the appropriate pair of wires to the igniter of the next mortar which was positioned immediately below the mortar just fired. The second mortar is accordingly fired and the pyrotechnic fuse of this mortar will usually be designed to permit the mortar to travel further from the launch point than the first mortar before it generates infra-red radiation. Subsequent firing pulses similarly cause the stepping switch to apply pulses in turn to the igniters of the remaining mortars yet to be fired, the pyrotechnic fuses of which will usually be designed to enable the mortars to travel pyrogressively greater distances than the mortars previously fired so that an approaching heat-seeking missile will be diverted away from the potential missile target.
One of the problems with such mortar firing systems is that short-circuiting of any of the aforesaid pairs of wires over which firing pulses are applied to the igniters of the mortars or shorting of the igniter itself can prevent operation of the stepping switch to its next outlet for firing the next mortar in the multiple pack. Consequently, the entire mortar pack or a part thereof may be rendered useless by such short-circuiting which will most likely occur as a result of fusing together of the ends of the aforesaid pairs of wires by the heat generated by the appertaining mortar igniter as the mortar is fired. The fusing together of these wire ends then prevents the re-operation of the stepping switch to apply the next incoming firing pulse to the next mortar to be fired.